php - 如何在下拉选择菜单上添加验证？

Question

如何在下拉选择菜单上添加验证我有代码并且我正在处理但问题是它不起作用没有显示错误消息。如果在单击添加到购物车按钮之前不应该选择下拉选择值，我想显示错误消息？

if(isset($_REQUEST['check'])){
if (isset($_POST['size']) && $_POST['size'] == '' ) {
echo 'Error, select category';
exit;
}}

<form action="" id="size1" name="size1" method="post"> 
<select style="background-color:#CCC" 
name="size" id="size"  onchange="this.form.submit();" >
<option value="">Select</option>
<option <?php if ($_POST['size'] == 'Small') 
print 'selected '; ?>  value="Small">Small</option>
<option <?php if ($_POST['size'] == 'Medium') 
print 'selected '; ?> value="Medium">Medium</option>
<option  <?php if ($_POST['size'] == 'Large') 
print 'selected '; ?> value="Large">Large</option>
<option   <?php if ($_POST['size'] == 'XL')
print 'selected '; ?> value="XL">XL</option>
</select>

<input type="button" class="button1" name="check" 
value="Add To Cart" onclick="addtocart(<?php echo $row3['id'];?>);" />
</form

Answer 1

请尝试它的工作

应该是这样的

<?php
    if($_POST['country']=="0")
    {
        echo 'Error, select category';
        //exit;
    }
?>
<form action="" id="size1" name="size1" method="post">
<select style="background-color:#CCC" 
name="size" id="size"  onchange="this.form.submit();" >
  <option value="0">Select</option>
  <option <?php if ($_POST['size'] == 'Small') 
print 'selected '; ?>  value="Small">Small</option>
  <option <?php if ($_POST['size'] == 'Medium') 
print 'selected '; ?> value="Medium">Medium</option>
  <option  <?php if ($_POST['size'] == 'Large') 
print 'selected '; ?> value="Large">Large</option>
  <option   <?php if ($_POST['size'] == 'XL')
print 'selected '; ?> value="XL">XL</option>
</select>
<input type="button" class="button1" name="check" 
value="Add To Cart" onclick="addtocart(<?php echo $row3['id'];?>);" />
</form>

Answer 2

如果我的问题正确，您希望在提交表单之前进行验证？如果是这样，那么您需要使用客户端验证：

http://docs.jquery.com/Plugins/validation#Example

Answer 3

在这里对 html 做些小改动

<option value="0">Select</option>

并像这样检查

function check_selected_or_not(){
var check_selected = jQuery('#size').val();
if (check_selected == 0){
    alert('Please select');
}else{
    alert('sucess');
}

}